The present invention relates generally to tissue scaffolds seeded with reparative cell populations for tissue repair, including myocardial repair. Without limiting the scope of the invention, its background is described in connection with existing methods and compositions of implantable materials for treating physical defects and wound healing.
Roughly 1% of humans are born with an atrial septal defect (ASD) which permits a shunt between the right and left atrium. Other deficiencies include ventricular septum defects and patent foramen ovale (PFO). Each of these defects are amenable to treatment by occlusion either by direct surgical techniques in suturing a patch or by placement of an occluder non-invasively. Current occluders and patch materials include non-absorbable but biocompatible materials such as polytetrafluroethylene (PTFE or Teflon® patches such as the GORE HELEX® Septal Occluder), woven polyester (Dacron® fabric disk devices such as CardioSEAL® and STARFlex®), stainless steel and polyurethane (i.e. the Sideris buttoned devices), nickel titanium shape memory alloys (i.e. the Amplatzer septal occluder constructed of a mesh of Nitinol wires) or cobalt-chromium-nickel alloys (Elgiloy). Although the synthetic patches are not absorbed, they act as a scaffold onto which normal tissue can grow and cover the defect, which is essentially “scarred” into place after about 3-6 months depending on the conditions of the defect.
For wound healing and reconstructive surgery, existing materials include the use of synthetic materials as well as biomaterials generated from human and other animal tissues, such as for example the acellular dermal matrices (ADM) derived from normal human skin (i.e. Alloderm® ADMs, also detailed in U.S. Pat. No. 7,358,284). Synthesized biodegradable scaffolds for tissue repair have been introduced for potential applications including tissue formation, expansion of host bone cells, cell transplantation, and bioactive molecule delivery. Preformed biodegradable scaffolds composed of polyglycolic acid (PGA) and poly L-lactic acid (PLLA) have been FDA-approved (i.e. Vicryl® polyglactin woven mesh). The biodegradable graft material, Dermagraft®, which has been approved for treatment of diabetic foot ulcers, is manufactured by seeding a polyglactin mesh with human fibroblasts which proliferate and coat the mesh with dermal collagen, matrix proteins, and growth factors before the mesh is cryopreserved.
The field of regenerative medicine has been extensively studying the potential of cell therapy for repair of injured or diseased tissue. To date, cells from multiple sources including embryonic stem cells, bone marrow derived mesenchymal stem cells, peripheral blood derived endothelial progenitor cells and mesenchymal stem cells, and selected adipose derived cells have been demonstrated to enhance tissue repair in one or more experimental models. Translation of these preclinical findings into a practical therapy is the subject of significant research. Since these research efforts are largely based on the premise that a single cell type, for example a pluripotent or totipotent stem cell, is the best choice for cell therapy, significant effort has been focused on identifying and then obtaining the target cell type.
It has been suggested that the post-graft mechanical behavior of ADM could be enhanced by cell seeding prior to implantation. (Erdag G, Sheridan R L. “Fibroblasts improve performance of cultured composite skin substitutes on athymic mice.” Burns 30(4) (2004) 322e8; Fuchs J R, et al. “Diaphragmatic reconstruction with autologous tendon engineered from mesenchymal amniocytes” J Pediatr Surg 39(6) (2004) 834-8). Tissue engineering involving the delivery of autologous stem cells and progenitor cells seeded on scaffolds is currently at the animal discovery stage and involves the seeding of scaffolds followed by in vitro culture to produce relatively large pieces of tissue prior to implantation. Such pre-seeded and cultured scaffolds have been shown to be of value for tissue repair in animal models.
Recent research in the inventor's laboratories has proven that a mixture of early mesenchymal, multi-potent, lineage committed and lineage uncommitted stem/progenitor cells and fully differentiated cells can be obtained from many body tissue areas. The early mesenchymal uncommitted cells originate from the microvessels within the tissues. For practical reasons, adipose tissue is a source that is available in most animal and human species without disrupting the physiological functions of the body. It has been reported that adipose derived stromal cells seeded onto carrier bioprosthetics facilitated formation of new bone in an animal model. (Cowan C M, et al. “Adipose-derived adult stromal cells heal critical-size mouse calvarial defects” Nat Biotechnol 22(5) (2004) 560e7).
Typically, cells for matrix or scaffold seeding are isolated from donor tissue and cultured for an extended period of time. For example, the FDA approved Apligraf® skin grafts available from Organogenesis (Canton, Mass.) are manufactured by first forming a bovine collagen matrix which is plated with cultured human dermal fibroblasts isolated from human donor skin. Certain aspects of the manufacturing process are disclosed in Bell, U.S. Pat. No. 5,800,537. The donor fibroblasts are cultured on the collagen matrix for 6 days to form a dermal matrix. Next the dermal matrix is plated with cultured human keratinocytes to promote development of a stratum corneum layer. The entire process takes from 20 to 27 days prior to packaging. While useful, such a process does not utilize pluripotent cells and is clearly not amendable to a point of care process employing the patient's own (autologous) cells. Additionally, recent findings suggest that the cells do not survive long term and engraft in the recipient patient thus limiting the utility of this allogenic cell product (Griffiths M, et al, “Survival of Apligraf in acute human wounds” Tissue Eng 10(7-8) (2004) 1180).
Alternatively, in research applications, bone marrow aspirate cells have been obtained from patients and the cells have been held in place or physically “trapped” on the matrix by an artificial means such as by a thrombin induced clot for holding bone marrow aspirate onto an osteogenic matrix. While these methods may have some utility, they require a prolonged treatment program including several surgical interventions.
Methods and compositions for the generation of point-of-care cell seeded matrices have not been heretofore available and there continues to be an unmet need for implantable cell seeded matrices that maybe generated in a single procedure. Also needed are methods and apparatus that permit the isolation of reparative cell populations that are suitable for direct seeding on to biocompatible matrices.
The present invention provides methods and materials for the focal application of reparative cell populations, for example for repair of damaged neurons, muscle, tendons, joints and bone structures, repair of parenchymal organs such as liver, kidney, heart, or brain, and for repair of skin tissues including in the treatment of burns, hernias, and non-healing wounds. Methods and materials are provided to retain desirable cell populations on biocompatible scaffolds and to most effectively use the scaffold in conjunction with a fresh cellular preparation, which avoids a need to culture the cells.